Realistic Car back lights [Cycles]
Final image with Compositing:



Different Color Ramp and Mapping node setups.



Scene overview:

Scene has three elements Emission source, Glass mesh and mesh to enclosed both of them. Also HDRI lightning.



Emission source:

Three Spheres with Emission shader mixed with Transparent (pure white, #FFF) by Light Path > is Camera Ray. We don't want to see'em.



Glass mesh and material:

Material:

Most important thing here. It's colored Transparent Shader mixed with Glossy by Layer Weight to have glass like reflection and to let light go trough. Don't forget to set Mapping node accordingly to your mesh.

You can control how much white, orange and red color you want.



Mesh:

This is just quick mesh created with Poke Face.



Final thoughts:

I've used also Glare node in Compositing to have nicer overall look.



Blend file:

Without HDRI lightning.